1-D P- and S-wave velocity models for the collision zone between the northern Tianshan mountain and the Junggar basin based on local earthquake data

We have developed crustal minimum 1-D P- and S-wave velocity models of the collision zone between the northern Tianshan mountain and the Junggar basin (86°E–89°E, 43°N–44.5°N). These two models were created through inversion of 1 370 P- and 1 396 S-wave travel times from 173 well-constrained local earthquakes recorded by the Ürümqi sparse local seismic network and temporary seismic arrays. In contrast to previous models, our results indicate relatively low velocity at both shallow (<10 km) and deep (30–45 km) depths. The shallow zone is interpreted to be the result of thick surficial sedimentary deposits, whereas the deeper anomaly is interpreted to result from ductile shearing and lower crustal flow. Additionally, we detected several transition layers under the lower crust, which may imply structural complexity of the uppermost mantle in this region. The improved models reduce the RMS residual of earthquake locations by 41.7% from 1.2 to 0.5 seconds. The more accurately located hypocenters appear to correlate with prominent local over-thrusts, which underlie an anticlinal fold belt and several blind faults. Positive station corrections are observed near the Junggar basin, which likely reflects low wave velocity; negative corrections near the Tianshan mountain and Bogda mountain suggest high wave velocity.National Natural Science Foundation (China) (Grant 41204037)China Earthquake Administration (Basic Research Project Grant 2012IES010103

Crustal structure of the central Tibetan plateau and geological interpretation

Based on teleseismic data obtained from 225 stations from two networks in the central Tibetan plateau, we have generated detailed crustal structure images using P-wave receiver function techniques with more accurate piercing-depth-correction and time-depth-correction than what have previously been available. Our images indicate an undulatory Moho beneath the Tibetan plateau with a steep jump beneath the northern Himalaya, and obviously different structures in proximity to the Bangong-Nujiang suture. In several sections of the Tibetan plateau, the lower crust is characterized by pervasive high-velocity regions, which are consistent with the preservation of eclogite bodies beneath the plateau, whose presence affects the dynamics of the Tibetan plateau.China Earthquake Administration (Grant 201308013)National Natural Science Foundation (China) (Grants 40974034, 41174086, 41074052 and 41021003

Depth determination of the Moho interface beneath the Tibetan plateau and other areas of China

We apply the adaptive moving window method of Sun et al. to the most recent catalog data and the data recorded by portable stations to construct the velocity structure of the crust and upper mantle, and to determine the depth of the Moho interface beneath the Tibetan plateau and other areas of China. We first select 2 600 locations in the study region with 1° intervals, then at each location invert for a five-layer 1-D P-wave velocity model from the surface down to the uppermost mantle by performing a Monte Carlo random search. The Moho depth at each location is then determined, and the Moho interface beneath the study region is obtained through proper interpolation with certain smoothing. Compared to depths obtained by previous studies, our results show more accurate Moho depths in the Tibetan plateau, Tianshan region and other areas of the study region.United States. Defense Threat Reduction Agency (Contract DTRA01-00-C-0024)Chinese Academy of Sciences (Fund KJCX2-EW-121

Crustal and uppermost mantle structure of Caucasus and surrounding regions

A 3-D P-wave velocity model is developed for the crust and uppermost mantle of Caucasus and the surrounding area by applying the tomographic method of Zhao et al. using 300 000 high-quality P-wave first arrivals from 43 000 events between 1964 and 2005. This tomographic method can accommodate velocity discontinuities such as the Moho in addition to smooth velocity variations. The spatial resolution is 1°×1° in the horizontal direction and 10 km in depth. The velocity images of the upper crust correspond well with the surface geology. Beneath the southern Caucasus high velocity anomalies are found in the middle crust and low velocity anomalies are found in the uppermost mantle. Relatively low Pn velocities are located under the Lesser Caucasus, eastern Turkey, and northern Iran. Higher Pn velocities occur under the eastern portion of the Black Sea and the southern Caspian Sea, and also extend into the eastern edge of Azerbaijan. Tomographic model significantly reduces the travel-time residuals.United States. Defense Threat Reduction Agency (Contracts DE-AC-52-04NA25612, NNSA-03-2S2 and W-7405-ENG-483)Chinese Academy of Sciences (Fund KJCX2-EW-121

Investigations of the b-value and its variations on possible earthquake prediction in the North-South China Seismic Belt

Thesis: S.M. in Geophysics, Massachusetts Institute of Technology, Department of Earth, Atmospheric, and Planetary Sciences, 2016.Cataloged from PDF version of thesis.Includes bibliographical references (pages 113-118).The Gutenberg-Richter b-value is studied extensively by researchers as a possible earthquake precursor. In this thesis, two different approaches to compute the b-value for the purpose of earthquake prediction are investigated and discussed. A new methodology, the b-value ratio method, inspired by a 1988 paper by Morgan et al., is also introduced in this thesis as a variation of b-value. To calculate the b-value ratio, the event catalog has to be separated into a group of larger events and a group of smaller events with a change-point magnitude, which leads to two b-values for the catalog, b-value of the smaller events, b-low, and the b-value of the larger events, b-high. The b-value ratio is then obtained by dividing b-high by b-low. Both b-value and b-value ratio methods are applied to a set of earthquakes occurring between 1983 and 2015 in the North-South China Seismic Belt. The dataset contains 4454 events for M >/= 3.6. Within this dataset, there is the catastrophic 2008 M = 7.9 Wenchuan earthquake. The b-value time series are computed in two different ways, the time-based method and the event-based method. Moving windows and overlapping windows are used in both ways. Our results calculated with the event-based method show an initial increase in b-value followed by a constant-slope decrease prior to the 2008 Wenchuan event. After the 2008 large earthquake occurred, the b-value bounces back to about 1.0 and starts to decrease again. The b-value ratio shows a completely reversed trend. Both b-value and b-value ratio in this case could be used as post-prediction precursors of the 2008 M = 7.9 Wenchuan earthquake. Analysis of b-value versus depth in the North-South China Seismic Belt region shows a monotonic decrease in b-value between 8km and 13km depth, which reflects an increase in differential stress in the upper crust. It is observed that b-value increases between 13 km and 22 km depth and decreases below 22 km depth. These observations correspond to the changes in the stress regimes and indicates the inverse relationship between b-value and differential stress in the crust.by Diming Yu.S.M. in Geophysic

Recent Advances of Organ-on-a-Chip in Cancer Modeling Research

Although many studies have focused on oncology and therapeutics in cancer, cancer remains one of the leading causes of death worldwide. Due to the unclear molecular mechanism and complex in vivo microenvironment of tumors, it is challenging to reveal the nature of cancer and develop effective therapeutics. Therefore, the development of new methods to explore the role of heterogeneous TME in individual patients’ cancer drug response is urgently needed and critical for the effective therapeutic management of cancer. The organ-on-chip (OoC) platform, which integrates the technology of 3D cell culture, tissue engineering, and microfluidics, is emerging as a new method to simulate the critical structures of the in vivo tumor microenvironment and functional characteristics. It overcomes the failure of traditional 2D/3D cell culture models and preclinical animal models to completely replicate the complex TME of human tumors. As a brand-new technology, OoC is of great significance for the realization of personalized treatment and the development of new drugs. This review discusses the recent advances of OoC in cancer biology studies. It focuses on the design principles of OoC devices and associated applications in cancer modeling. The challenges for the future development of this field are also summarized in this review. This review displays the broad applications of OoC technique and has reference value for oncology development